Superabsorbers are water-insoluble crosslinked polymers which are capable of absorbing and retaining under pressure large amounts of aqueous liquids, in particular body fluids, preferably urine or blood, with swelling and formation of hydrogels. In general, these uptakes of liquid are an amount of water at least 10 times or even at least 100 times the dry weight of the superabsorbers or superabsorbent compositions. Due to these characteristic properties, these polymers are mainly used in sanitary articles, such as baby nappies, incontinence products or sanitary towels. A comprehensive overview of superabsorbers and superabsorbent compositions, their use and their preparation is given by F. L. Buchholz and A. T. Graham (editors) in “Modern Superabsorbent Polymer Technology”, Wiley-VCH, New York, 1998.
Superabsorbers are as a rule prepared by free radical polymerization of usually partly neutralized monomers carrying acid groups in the presence of crosslinking agents. In this context, polymers having different absorption properties can be prepared, according to the choice of the monomer composition, the crosslinking agents as well as the polymerization conditions and the processing conditions for the hydrogel obtained after the polymerization. Further possibilities are offered by the preparation of graft polymers, for example using chemically modified starch, cellulose and polyvinyl alcohol in accordance with DE-OS 26 12 846.
DE 40 20 780 C1 discloses the after-treatment of superabsorbent polymers by post-crosslinking of the surfaces of the polymer particles. By the post-crosslinking of the surface of the water-absorbing polymer particles, the absorption capacity of the polymer particles under the action of pressures is increased in particular.
DE 199 09 653 A1 and DE 199 09 838 A1 describe pulverulent polymers which are post-crosslinked on the surface and absorb water, aqueous or serous liquids or blood, and which are based on monomers carrying acid groups and have been coated with a surface post-crosslinking agent and a cation in aqueous solution and post-crosslinked. The polymers disclosed in this prior art have advantageous absorption properties compared with conventional polymers, in particular a high permeability.
During more prolonged wearing of hygiene articles which contain absorbent polymers and which have already partly absorbed body fluids, such as urine, or during storage of used nappies, such as is usual, for example, in hospitals, an unpleasant odor nuisance may immediately occur due to the organic constituents of the urine and the body heat of the person wearing the article. To counteract this, numerous attempts have been made to achieve binding of the odor-forming substances by appropriate admixtures in the constituents of the hygiene article other than the superabsorber, or to cover up the odor by perfumes or the like. The introduction of such substances in the form of constituents other than superabsorbers often has a negative effect on the performance of these hygiene articles during wearing. Thus, the odor-inhibiting or odor-reducing substances which are initially present spatially separated from the superabsorber region are often introduced by the body fluids into the superabsorber-containing region of a hygiene article, for example by washing in, where they then have a negative effect on the performance of the superabsorber and therefore of the hygiene article overall. A further disadvantage of this concept is that the majority of the body fluid released into the hygiene article is in any case in the superabsorber, and the odor-inhibiting or odor-reducing substances outside the superabsorber can display their action less efficiently.
DE 198 25 486 A1 and DE 199 39 662 A1 disclose the combination of superabsorbers with cyclodextrin for reducing odor. However, it is to be seen from this highly promising approach that the cyclodextrin shows its odor-inhibiting action in the superabsorber only under certain conditions, namely when it is ensured that the cyclodextrin does not separate again from the superabsorber. It is preferable here for the cyclodextrin to be incorporated at least into the surface of the superabsorber article by the cyclodextrin and/or cyclodextrin derivatives being covalently and/or ionically bonded and/or enclosed therein.
DE 103 34 271 A1 furthermore discloses superabsorber agglomerates which can contain a large number of odor-binding substances homogeneously in the agglomerate. However, this specification, which discloses an outstanding solution for the use of superabsorber fine particles, provides no superabsorbers having odor-binding properties which are particularly suitable for use in hygiene articles. Thus, in addition to an efficient and effective use of the odor-binding substances, the superabsorber properties influenced by these odor-binding substances are still in need of improvement.
DE 10 2005 055 497 A1 teaches that superabsorbent polymers are provided with improved odor-binding properties by bringing them into contact with metal salts of ricinoleic acid, optionally in combination with amino acids to improve solubility.
In general, the present invention was based on the object of moderating or even overcoming the disadvantages emerging from the prior art.